Habitat

The microdistribution of any species relates to habitat preference. The Northeast Pacific distribution of most cot-toid species is reflected in an analysis of fish community structure of rocky shorelines of the North Pacific, which is dominated by cottids. The rocky intertidal of the Pacific coast of North America is dominated by various species of Artedius, Clinocottus, and Oligocottus. Other cottid genera have very narrow depth preferences in shallow subtidal marine waters. For example, the longfin sculpin, Jordania zonope, was considered extremely rare prior to the advent of scuba diving, because it inhabits vertical rock surfaces that are not amenable to sampling with nets. Similarly, the manacled sculpin, Synchirus gilli, was considered very rare until divers discovered it on the feather boa kelp, Egregia menziesi, on outer Pacific coast shores. The feather boa kelp does not occur, however, in protected inland seas like the Strait of Georgia (British Columbia), where the manacled sculpin spawns in the holdfasts of another kelp species, Alaria marginata. For the majority of cottoid species, very little is known of precise habits and habitat preferences.

The diverse snailfishes (Liparididae) occur broadly in the world ocean over a very wide depth range from the intertidal zone to greater than 23,000 ft (7,010 m) depth. Again, very little precise habitat information is available for the vast ma jority of species. Since most snailfishes possess a pelvic sucking disc, however, it is presumed that smooth surfaces of plants, animals, or rocks provide substrate for many of these species. As with other cottoid fishes, different species may prefer shores exposed to waves and tidal currents versus protected shores.

The Lake Baikal sculpins have been investigated since the eighteenth century. The diversification of these species seems in great part related to different depth preferences. Lake Baikal, at 5,315 ft (1,620 m) depth, is the deepest lake in the world.

The reason why the less diverse freshwater cottoid fishes have been studied more intensely than the vast diversity of marine species is that freshwater habitats are more accessible. Perhaps the most accessible marine habitat is the tidepool, and intertidal cottoids have received disproportionate study, except in comparison with fish species of commercial importance. A problem with the study and interpretation of tide-pool fishes, however, has to do with the human perspective. Since people can most readily work around tidepools during low tides and calm weather, our interpretation of tidepools tends to focus on ecological advantages of the tidepool during a low tide (in calm weather) rather than during high tides and storms. Thus, tidepools are considered to offer refuge from subtidal predators during low tides, rather than to offer refuge from turbulence during high tides. Habitat can have widely divergent values and characteristics under different conditions, so the interpretation of habitat preferences needs to be tempered by perspective.

Discussions of fish habitat implicitly consider only adults in most studies. Tidepool studies reveal, however, that early juvenile stages of cottid species can have different habitat requirements than adults. Larval stages occupy the planktonic realm, a completely different habitat than that of most adult cottoids. Larvae of rocky intertidal cottids of various species have been shown to avoid drifting with currents away from the shoreline or along the shoreline, so behavior during early life stages may be directed toward providing access to required habitat in later stages. The precise substrate preference of a cottoid larva at settlement from the plankton may not be the same substrate preference as an adult, but it will be a substrate that is a component of the adult habitat. Thus, growth stages shift only their relative position on the seabed within a general habitat.

Niche partitioning between species in terms of habitat preference (as with food preference) is examined for mechanisms that allow ecological separation that could have led to speciation. Again, interpretation often focuses only on adults. In addition, intertidal studies of cottids have led to different interpretations of competition than subtidal studies. The flat-head sculpin, Artedius lateralis, and the padded sculpin, Arte-dius fenestralis, occupy very similar habitats in the rocky intertidal, yet their larvae occupy different depth ranges along the shoreline. The flathead sculpin settles from the plankton in surface waters, directly onto substrates in the intertidal, whereas larvae of the padded sculpin occupy slightly deeper water, so that they settle subtidally. Thus, habitat preferences in terms of depth provide ecological segregation of these two cottid species during the larval and early juve nile stages. Adults of these species do not necessarily have to display any behavioral differentiation in order for their spe-ciation to be explained.

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